Porous silicon that strongly emits in the visible was analyzed using Raman scattering. The spectrum peaks near 508 cm ~ ', has a width of-40 cm I~ ', and is very asymmetric. Using a model of phonon confinement, this suggests that the local structure of porous silicon is more like a sphere than a rod and has a characteristic diameter of 2.5-3.0 nm. Polarization Raman measurements suggest that the structure does not consist of a series of parallel columns.
The
distributions and reductions of volatile organic compounds
(VOCs; alkanes, aromatics, and halogenated hydrocarbons) emitted from
two coal-fired power plants were compared. The partial removal of
VOCs by air pollution control devices meant to reduce NO
x
, particulate matter, and SO
x
was assessed. The data show that VOC levels in flue gas were
reduced by 5–35% after selective catalytic reduction, 0–40%
after air preheating and electrostatic precipitation, and 10–20%
after flue gas desulfurization and wet electrostatic precipitation.
Adding modified fly ash was found to further reduce the effluent concentration
of VOCs by 10–20%, resulting in an overall VOC reduction of
40–80%. This decrease in emissions is attributed to oxidation,
deposition, condensation, and water absorption mechanisms.
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